dpaa_eth: try to move the data in place for the A050385 erratum

The XDP frame's headroom might be large enough to accommodate the
xdpf backpointer as well as shifting the data to an aligned address.

Try this first before resorting to allocating a new buffer and copying
the data.
Suggested-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Acked-by: Madalin Bucur <madalin.bucur@oss.nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/dpaa/dpaa_eth.c

@@ -2180,8 +2180,9 @@ static int dpaa_a050385_wa_xdpf(struct dpaa_priv *priv,
 				struct xdp_frame **init_xdpf)
 {
 	struct xdp_frame *new_xdpf, *xdpf = *init_xdpf;
-	void *new_buff;
+	void *new_buff, *aligned_data;
 	struct page *p;
+	u32 data_shift;
 	int headroom;
 
 	/* Check the data alignment and make sure the headroom is large
@@ -2198,6 +2199,23 @@ static int dpaa_a050385_wa_xdpf(struct dpaa_priv *priv,
 		return 0;
 	}
 
+	/* Try to move the data inside the buffer just enough to align it and
+	 * store the xdpf backpointer. If the available headroom isn't large
+	 * enough, resort to allocating a new buffer and copying the data.
+	 */
+	aligned_data = PTR_ALIGN_DOWN(xdpf->data, DPAA_FD_DATA_ALIGNMENT);
+	data_shift = xdpf->data - aligned_data;
+
+	/* The XDP frame's headroom needs to be large enough to accommodate
+	 * shifting the data as well as storing the xdpf backpointer.
+	 */
+	if (xdpf->headroom  >= data_shift + priv->tx_headroom) {
+		memmove(aligned_data, xdpf->data, xdpf->len);
+		xdpf->data = aligned_data;
+		xdpf->headroom = priv->tx_headroom;
+		return 0;
+	}
+
 	/* The new xdp_frame is stored in the new buffer. Reserve enough space
 	 * in the headroom for storing it along with the driver's private
 	 * info. The headroom needs to be aligned to DPAA_FD_DATA_ALIGNMENT to